Compressor air bleed control



Dec. 9, 1958 B. N. TORELL COMPRESSOR AIR BLEED CONTROL Filed May 3, 1954 INVENTOR BRUCE N TORELL B) AJLpQM M A T TOPNEV COMPRESSOR AIR BLEED CONTROL Bruce N. Tor-ell, Wethersfield, Conn, assignor to United Aircraft Corporation, East Hartford, Conn, a corporatron of Delaware Application May 3, 1954, Serial No. 427,304 6 Claims. (Cl. 230-114) This invention relates to a bleed control for a multi stage axial-flow compressor and particularly to an arrangement by which to prevent aerodynamic stalling within the compressor.

One feature of the invention is an arrangement by which to control the amount of bleeding during compressor operation so that the compressor will operate close to the stall condition without stalling. Another feature is an arrangement by which to vary the amount of bleed air as a function of the ratio of absolute compressor discharge pressure or its equivalent divided by compressor inlet total pressure less compressor inlet static pressure.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawing which illustrates an embodiment of the invention.

The single figure is a diagrammatical showing of the control.

. The invention is shown in connection with a multistage axial-fiow compressor 2 in which a number of low pressure stages or rows of blades 4 are carried by one rotor 6 .and the remaining stages, referred to as high pressure stages, or rows of blades 8 are carried by a second rotor 10. Each of the rotors is separately driven from the separate rotors 12 and 14 of a multi-stage turbine, the high pressure compressor rotor and the high pressure turbine rotor being connected by a sleeve 16 and the low pressure compressor and turbine rotors being connected by .a shaft 18.

For improving the partial load operation of the compressor and to facilitate starting, a bleed is provided be tween the ends of the compressors. In the arrangement shown, the bleeding takes place between the low and high compressor pressure rotors. To provide for this bleeding, the casing 20 which supports the rows of stator vanes 22 that alternate with the rows of blades, has a surrounding ring 24 thereon defining an annular chamber 26 communicating with one or more radial passages 28 extending through the casing. These passages provide for air flow from the air path through the compressor into the chamber 26.

A cylinder 30 mounted on the outside of the ring 24 and communicating with the chamber has positioned therein a valve 32 by which to control the amount of air vented from the chamber 26 and thereby controlling the amount of air bled from the compressor. This valve may be moved under fluid pressure between its open and closed positions, as for example, by a piston 34 connected by a rod 36 and link 38 to an arm 40 on the valve. The piston 34 is located in a cylinder 42, the opposite ends of which are connected by conduits 44 to a pilot valve 46 slidable in a bore 48 in a control casing 50. Air under pressure, through a passage 52 in the casing, enters the bore 48 through an inlet port 54 located midway between the outlet ports 56 and 58 which are connected to the conduits 44. Spaced lands 60 and 62 on the valve 46 cover the *ports 56 and 58 when the valve is in the mid position 'nited States Patent r 2,863,601 Ca Patented Dec. 9, 1958 shown. If the valve is shifted in either direction, one of the outlet ports will be placed in communication with the inlet port 54 and the other outlet port will be connected to a vent hereinafter described.

The valve 46 is moved in response to pressure changes in the power plant. To accomplish this, the valve has integral extensions at each end connected to diaphragms 64 and 66 located in enlargements 68 and 70 at opposite ends of the casing 50. The diaphragm 64 defines a chamber 72 to the left of the diaphragm and another chamber 74 to the right of the diaphragm. Similarly, diaphragm 66 has a chamber 76 to the right of the diaphragm and another chamber 78 at the left of the diaphragm. The chambers 74 and 78 which are located on the inner sides of the diaphragms are vented to the atmosphere through ports 80 and 82 respectively.

The chamber 72 to the left of the diaphragm 64 is connected as by a conduit 84 to a static pressure tap 86 in the compressor inlet such that the diaphragm 64 is subjected to static compressor inlet pressure. The chamber 76 to the right of the diaphragm 66 is connected by a conduit 88 to a total pressure probe 90 also positioned in the compressor inlet such that the diaphragm 66 is subjected to the total compressor inlet pressure.

Pilot valve 46 has mounted therein a piston 92 fitting in a cylinder 94 in the casing 50. The left hand side of the piston 92 is subjected to total compressor discharge pressure from a total pressure probe 96 located in the discharge of the compressor. This probe -is connected by a duct 96 to a chamber 100 and thence through a conduit 102 to the cylinder 94. The chamber 100 has a discharge nozzle 104 through which air within the chamber expands to ambient or atmospheric pressure, a nd the pressure at the nozzle throat is transmitted through a conduit 106 to the cylinder 94 at the right of the piston 92. The nozzle constitutes a sonic nozzle since the velocity of the air through the throat will be sonic.

The control arrangement is such that the bleed valve 32 can adjust the quantity of bleed air so as to limit the ratio between the absolute compressor discharge pressure, i. e., compressor discharge pressure plus ambient pressure, and the difference between total compressor inlet pressure and static compressor inlet pressure to a fixed value. This limit would represent a sinlge line on a plot of compressor pressure ratio against corrected inlet air flow. By selecting a proper fixed value for the ratio this line would be made to fall directly below and parallel to the compressor stall line.

The control obtains a measure of absolute compressor discharge pressure by expanding a small quantity of air through nozzle 104 to ambient pressure and measuring the ditference between the total compressor discharge pressure and the static pressure at the nozzle throat. Since the pressure ratio across the nozzle will always be above the critical value, that is the pressure ratio value producing a constant velocity at the throat equal to the velocity of sound, the difference, therefore, between total compresor discharge pressure (Pt and static pressure at the throat (Pth) will be proportional to the absolute compressor discharge pressure (Ptg That is to say, P1 minus Pth is proportional to Pt With the arrangement shown, valve 46 will move to the right to open the bleed valve 32 if the desired ratio between total compressor discharge pressure (Pt minus throat pressure (Pth) and total compressor inlet pressure (Pt minus static compressor inlet pressure (PS2), that is is exceeded. This opening of the bleed valve reduces the value of this ratio until the desired limiting value is reached thereby restoring valve 46 to tion.

Conversely, at ratios of Pz 'Pth PER-PS2 In this way it is apparent that the bleed valve is moved in response to changes in the ratio of the difference between its neutral positotal compressor discharge pressure and. another pressure I which will be proportional-to absolute compressor discharge pressure and the difference between total compressor inlet pressure and static compressor inlet pressure. That isto say, Pt Pt and Pt Pth are both propor tional to P1 which is the pressure selected for the ratio to which the bleed valve is controlled.

It is to be understood that the invention is not limited to the specific embodiment herein illustrated and described, but may be used in other Ways without departure from its spirit as defined by the following claims.

I claim:

1. A multi-stage compressor having means for bleeding an intermediate stage thereof and means for varying the area of said bleeding means in combination With a bleed control comprising valve means, means connecting said compressor and said bleed control for actuating said valve as a function of absolute compressor discharge pressure, means connecting said compressor and said bleed control for actuating said valve as a function of compressor inlet total pressure, means connecting said compressor and said bleed control for actuating said valve as a function of compressor inlet static pressure, and means operatively connected with and controlled by the actuation of said valve to regulate said area varying means.

2. A multi-stage compressor having means for bleeding,

an intermediate stage thereof and means for varying the area of said bleeding means in combination with a bleed control comprising a housing having a shiftable valve therein, means connecting said compressor and said housing for shifting said valve as a function of absolute compressor dis-charge pressure, means connecting said compressor and said housing for shifting said valve asa function of compressor inlet total pressure, means connecting said compressor and said housing for shifting said-valve as a function of compressor inlet static pressure, and means operatively connected with and controlled bythe shifting of said valve to regulate said area varying means.

3. A multi-stage compressor having means for bleeding a stage thereof and means for varying the area of.said bleeding means in combination with a servomotor for actuatingsaid area varying means, said servomotor including a housing having a shiftable pilot valve therein, means for shifting said pilot valve in one direction as a function of compressor inlet total pressure, means for shifting said pilot valve "in the opposite direction as a function of compressor inlet static pressure, a sonic nozzle connected to the discharge of said compressor and discharging to the atmosphere, means for shifting said pilot valve in one direction as a function of the pressure upstream of said nozzle, means for shifting said pilot valve in the opposite direction as a function of the pressure at the throat of said nozzle, and means controlled by the shifting of said pilot valve to regulate said area varying means.

4. A multi-stage compressor having means for bleeding a stage thereof and means for varying the area of said bleeding means in combination with a servomotor for actuating said area varying means, said servomotor including a housing having a shiftable pilot valve therein, a sonic nozzle connected to the discharge of said compressor and discharging to the atmosphere, means for shifting said pilot valve in one direction as a function of compressor inlet static pressure and as a function of the pressure upstream of said sonic nozzle, means for shifting said pilot valve in the opposite direction as a function of compressor inlet total pressure and as a function of the pressure at the throat of said sonic nozzle to regulate said area varying means.

5; A multi-stage compressor comprising a low pressure rotor and a high pressure rotor, means for bleeding the compressor between the low pressure and high pressure rotors, means for varying the area of said bleeding means, a bleed control comprising valve means, means connecting said compressor and said bleed control for actuating said valve as a function of absolute compressor discharge pressure, means connecting said compressor and said bleed control for actuating said valve as a function of compressor inlet total pressure, means connecting said compressor and said bleed control for actuating said valve as a function of compressor inlet static pressure, and means operatively connected with and controlled by the actuation of said valve to regulate said area varying means.

6. A multi-stage compressor comprising a low pressureservomotor including a housing having a shiftable pilot valve therein, a sonic nozzle connected to the discharge of said compressor and discharging to the atmosphere, means for shifting said pilot valve in one direction as a function of compressor inlet static pressure and as a function of the pressure upstream of said sonic nozzle, and

means-for shifting said pilot valve in the opposite direction as a function of compressor inlet total pressure and as a function of the pressure at the throat of said sonic nozzle to regulate said area varying means.

References Cited in the file of this patent UNITED STATES PATENTS 1,110,864 Banner Sept. 15, 1914 2,398,619 Clark Apr. 16, 1946 2,463,865 Gilfillan Mar. 8, 1949 2,667,150 Coar Jan. 26, 1954 2,732,125 Ruby Jan. 24, 1956 FOREIGN PATENTS 190,121 Great Britain Mar. 31, 1924 214,954 Great Britain Sept. 4, 1924 278,324 Switzerland Ian. 16, 1952 

